1. Field
Methods and apparatuses consistent with the present inventive concept relate to receivers for digital television (DTV) signals transmitted by over-the-air broadcasting, which DTV signals include M/H signal components designed for reception by mobile receivers and hand-held receivers collectively referred to as “M/H receivers”.
2. Related Art
The Advanced Television Systems Committee (ATSC) published a DTV Standard in 1995 as Document A/53, hereinafter referred to simply as “A/53”. A/53 describes vestigial-sideband (VSB) amplitude modulation of the radio-frequency (RF) carrier wave using an eight-level modulating signal, which type of over-the-air DTV broadcasting is called “8-VSB”. In the beginning years of the twenty-first century, efforts were made by some in the DTV industry to provide for more robust transmission of data over broadcast DTV channels without unduly disrupting the operation of so-called “legacy” DTV receivers already in the field. Samsung Electronics Company, Ltd. (SEC) and LG Electronics (LGE) fielded robust transmission systems referred to as “A-VSB” and “MPH”, respectively, and each company vied for its system being accepted by ATSC as the basis for a TV-industry-wide standard robust transmission system. Robust transmission of data for reception by M/H receivers will be provided for in successive versions of an ATSC Standard for DTV broadcasting to M/H receivers, referred to more briefly as the M/H Standard. The initial version of this standard is the ATSC Mobile DTV Standard published by the ATSC in 2009 as Document A/153, hereinafter referred to simply as “A/153”, Parts 2 and 3 of which are incorporated herein by reference.
The operation of nearly all legacy DTV receivers is disrupted if 2/3 trellis coding is not preserved throughout every transmitted data field. Also, the average modulus of the transmitted DTV signal should be the same as for 8-VSB signal as specified in the 1995 version of A/53, so as not to disrupt adaptive equalization in those legacy receivers using the constant modulus algorithm (CMA).
Another problem concerning legacy DTV receivers is that a large number of such receivers were sold that were designed not to respond to broadcast DTV signals unless de-interleaved data fields recovered by trellis decoding were preponderantly filled with (207, 187) Reed-Solomon (RS) forward-error-correction (FEC) codewords of a specific type or correctable approximations to such codewords. Accordingly, in order to accommodate continuing DTV signal reception by such legacy receivers, robust transmissions are constrained in the following way. Before convolutional byte interleaving, data fields should be preponderantly filled with (207, 187) RS FEC codewords of the type specified in A/53.
This constraint has led to the M/H data encoded for reception by M/H receivers being encapsulated within (207, 187) RS FEC codewords of the general type specified in A/53, differing in that they are not necessarily systematic with the 20 parity bytes located at the conclusions of the codewords. The 20 parity bytes of some of these (207, 187) RS FEC codewords appear earlier in the codewords to accommodate the inclusion of training signals in the fields of interleaved data. The 207-byte RS FEC codewords invariably begin with a three-byte header similar to the second through fourth bytes of an MPEG-2 packet (as defined by the Moving Pictures Expert Group), with a 13-bit packet-identification (PID) code in the fourth through sixteenth bit positions of the header. Except for the three-byte header and the 20 parity bytes in each (207, 187) RS FEC codeword, the remainder of the codeword has been considered to be available for encapsulating 184 bytes of a robust transmission. (In actuality, the inventor notes, the last byte of the three-byte header of a 207-byte RS FEC codeword could also be replaced by another byte of M/H data, so a 207-byte RS FEC codeword could encapsulate 185 bytes of a robust transmission.)
In A/153, successive equal lengths of the M/H data stream are subjected to transversal Reed-Solomon (TRS) coding, and then to periodic cyclic redundancy check (CRC) coding to develop indications of the possible locations of byte errors in the TRS coding. These procedures are designed to correct byte errors caused by protracted burst noise, particularly as may arise from loss of received signal strength, and are performed in an apparatus called an “M/H Frame encoder”. An M/H Frame is a time interval that, at least usually, is of the same 968-millisecond duration as 20 8-VSB Frame intervals. The M/H Frame is sub-divided into five equal-length M/H Sub-Frames, each composed of sixteen successive Groups of M/H data, thereby defining eighty Slots for M/H data in each M/H Frame. The related M/H data within a selected set of the eighty Slots in an M/H Frame is referred to as a “Parade”. Each Parade is composed of one “Ensemble” or of two Ensembles located in different portions of Groups. Each Ensemble is TRS and CRC coded independently of every other Ensemble.
The output signal from the M/H frame encoder is supplied for subsequent serial concatenated convolutional coding (SCCC) of the general sort described by Valter Benedetto in U.S. Pat. No. 5,825,832 issued Oct. 20, 1998 and titled “Method and Device for the Reception of Symbols Affected by Inter-symbol Interference”. The encoder for the SCCC comprises an outer convolutional encoder, an interleaver for two-bit symbols generated by the outer convolutional encoder, and an inner convolutional encoder constituting the precoder and 2/3 trellis coder prescribed by A/53. Six sequences of known symbols are introduced into the SCCC within in each Group. This is done to help adaptive channel-equalization filtering in receivers for the M/H signals.
MPH was designed by LGE engineers to transmit an MPEG-2-compatible stream of 187-byte transport packets. However, in the ATSC subcommittees, it was decided to transmit indeterminate-length Internet-Protocol (IP) Transport Stream (TS) packets instead. The indeterminate-length IP packets cannot be parsed by simply referring to the beginnings of rows of bytes in the TRS frame. Accordingly, each of the rows of bytes in TRS frames begins with a 16-bit, two-byte header that includes an indication of where in the row an IP packet begins, if an IP packet begins in that row and is the first IP packet to begin in that row. If more than one IP packet begins in a row, the beginning of each further IP packet is reckoned from the packet length information contained in the header of the preceding IP packet. The header of each IP packet contains a 16-bit, two-byte checksum for CRC coding of that particular IP packet.
The IP signal supplied to the later stages of an M/H receiver includes SMT-MH packets, each transmitting a respective Service Map Table (SMT) for each Ensemble included in an M/H signal transmission. These SMT-MH packets are used for assembling an Electronic Service Guide (ESG) that is made available on a viewscreen for guiding a user of the M/H receiver in the user's selection of a sub-Channel to be received and the mode of reception of that sub-Channel. After such selection by the user, stored SMT-MH data is used for conditioning the operation of the receiver accordingly. Each SMT-MH packet includes indications therewithin as to whether the SMT-MH packet repeats the previous SMT-MH packet for the Ensemble or updates the previous SMT-MH packet. The repetition of SMT-MH packets was designed to make available an additional degree of protection of the SMT-MH data against corruption by noise.
In MPH, the SCCC was accompanied by two kinds of signaling channels. One is the Transmission Parameter Channel (TPC), and the other is the Fast Information Channel (FIC). TPC signaling immediately followed by FIC signaling is transmitted in every M/H Group—that is, twice in each 8 VSB data field, beginning in its 17th data segment and in its 173rd data segment. TPC and FIC information used 12-phase, quarter-rate parallelly concatenated convolutional coding (PCCC) as outer coding, followed by inner coding that continues the 2/3 trellis coding used in other portions of the DTV signal. TPC and FIC signaling continues to be specified in A/153 although modifications of such signaling have been made in regard to the specifics of its PCCC and to the specific syntaxes of the TPC data and the FIC data.
The TPC signaling conveys M/H transmission parameters such as various FEC modes and M/H frame information. The TPC information is (18, 10) Reed-Solomon coded, but is not interleaved. MPH used advanced TPC signaling, in which the TPC information for the next M/H Frame was transmitted in the final three sub-Frames of the current M/H Frame and in the initial two sub-Frames of that next M/H Frame.
The principal purpose of FIC signaling is to foretell the M/H Ensemble configuration, so the receiver can acquire the specific RS-Frame(s) associated with a particular broadcast service. The FIC information is (51, 37) Reed-Solomon coded, and the resulting 51-byte codewords are matrix block interleaved for transmission within the Groups in each sub-Frame. In order to de-interleave the block interleaving of the 51-byte FIC codewords, a receiver has to know the total number of Groups (TNoG) transmitted within each M/H sub-Frame. In MPH, as originally proposed, the receiver had to calculate TNoG by detecting and counting the occurrences of the training signal included in each Group within an M/H sub-Frame. Later on, however, TNoG information was incorporated into the syntax for TPC signals.
In MPH, each Chunk of FIC signaling descriptive of an entire M/H frame was limited to 560 bytes so it could be transmitted within a single sub-Frame. Each FIC-Chunk was divided into FIC-Segments that were transmitted within respective Groups of the sub-Frame. MPH used advanced FIC signaling, in which the FIC information for the next M/H Frame was transmitted in each of the final three sub-Frames #2, #3 and #4 of the current M/H Frame. The FIC information was also transmitted in each of the initial two sub-Frames #0 and #1 of that next M/H Frame. It was subsequently pointed out in an ATSC ad hoc group that FIC signaling may require more than 560 bytes when a broadcaster transmits more than 140 or so M/H services. In such case FIC signaling cannot be completed within a single M/H sub-Frame. Coherent Logix, Inc. proposed remedying this shortcoming by transmitting additional FIC information as part of the IP signals encoding M/H data transmitted by SCCC.
LGE and SEC made a joint counterproposal that FIC Chunks be extended to span plural sub-Frames, up to five in number, rather than just a single sub-Frame. LGE and SEC proposed that the header of the FIC-Chunk be located either in the penultimate sub-Frame of an M/H Frame or in its final sub-Frame. Then, if possible, the FIC-Chunk would be repeated with a header in the first, second or third sub-Frame of the succeeding M/H Frame. This joint proposal of LGE and SEC presumed the FIC-Chunk to be provided with a header containing a current_next_indicator bit indicating when set to ‘1’ that the FIC-Chunk would be currently applicable. The current_next_indicator bit when set to ‘0’ indicates that the FIC-Chunk would be applicable for the M/H Frame beginning next after the conclusion of the FIC-Chunk. In the latter case, the most recently occurring FIC-Chunk transmitted with the current_next_indicator bit set to ‘1’ should be currently applicable. The joint proposal further specified that the initial two bits of the header of each FIC-Segment which specify FIC_type would be 00 when the FIC-Segment contained a portion of an FIC-Chunk as proposed and would be 11 when the FIC-Segment was empty of FIC-Chunk data.